1. Field of the Invention
The present invention relates to a measuring tape device, in particular, it refers to a measuring tape device that has an automatic locking to mechanism.
2. Description of Prior Art
With the increasing demand for surveying, the measuring tape devices get to be more widely used. An early conventional measuring tape device comprises of a casing, there is a coilable tape contained inside the casing. At the center of the casing is a bobbin, one end of the tape is connected to the bobbin with a spring, and the other end of the tape extends out of the casing through an aperture. This type of measuring tape device does not have a locking mechanism, when a user release the distal end of the tape after the tape is extracted out of the casing, the tape is immediately retracted back into the casing, so it is inconvenient for the user to read the measurement on the tape.
According to Chinese Patent Publication (No. CN 2767951Y), in which it disclosed an utility model entitled “A measuring tape device with an automatic position locking”, the construction of the measuring tape device is as shown in FIG. 1, it comprises of a casing 1, in the center of which is a bobbin 4 that is connected to a spring. One end of a coilable tape 2 is connected to the bobbin 4 and is wound around the bobbin 4 inside the casing, while the other end of the tape extends out of casing 1 through an aperture that is formed on the lower end of the casing. Inside the casing near the location of the aperture is a stopper 3, the stopper 3 is positioned above the linear part of the tape 2 that reaches the aperture. At the upper end of the casing 1 is a button 5, the front end of the button 5 is a “J” shape extension piece, and the end of the “J” shape extension piece is settled against the back of the stopper 3. In between the casing 1 and the stopper 3 is a spring 6, the spring 6 is for exerting a force of restoration onto the stopper 3.
In its natural state, the stopper 3 is spring-loaded to be biased towards the tape 2, causing the stopper 3 to come in contact with the linear part of the tape 2, and thus exerting a friction against the tape 2, the tape 2 is then locked in place, and user can readily read the measurement on the tape. When the user need to retract the tape back into the casing, the user presses the button 5, so the stopper 3 is pushed by the “J” shape extension piece that is at the front end of the button 5, which causes the stopper 3 to depart from the tape 2, the tape 2 is then retracted back into the casing by the spring loading.
However, this kind of measuring tape device consists of too many components, so the structure of the device becomes too complicated, and the production cost becomes too high. Furthermore, since the locking mechanism of the measuring tape depends on the “J” shape extension piece at the front end of button 5 to move the stopper 3, if the contact between the “J” shape extension piece and the stopper 3 deteriorates due to extensive usage, the effectiveness of the locking mechanism of the measuring tape will be affected, which decreases the reliability of the locking mechanism.